Sure, its possible, but not exactly "easy" - you'll have to add some javascript code yourself to basically hook into the onload event handler for the document *or* add your code to the static "run" method in ZmZimbraMail (which does the same thing).

For example, you'll basically want to add something like this to the *end* of the run method:

Code:

var newWin = window.open("http://www.myurl.com", "_blank");

Any direct changes you make to javascript files means you'll also have to redeploy the webclient (under /ZimbraWebClient, run "ant prod-deploy").